SLAMF molecules are involved in the expression and regulation of multiple aspects ofthe innate and adaptive immune response. Work in mice carried out under the auspices of this Program have revealed important roles in the expression of autoimmunity, and more importantly, lupus-related pathology. Interestingly, disputed SLAMF-llnked single nucleotide polymorphism (SNP) associations have been reported in patients with systemic lupus erythematosus (SLE) while the expression of SLAMF isoforms and their modulatory role on immune cell function has not been studied systematically. We hypothesize that the expression of isoforms of SLAMF is aberrant in Immune cells in SLE patients and that their homotypic engagement leads to aberrant immune cell function including cytokine and autoantibodyproduction. To test this hypothesis we propose experiments grouped in four Specific Alms.